The present invention relates to the preparation of high impact polymers from vinyl aromatic compounds. More particularly, the present invention relates to the polymerization of vinyl aromatic hydrocarbons in the presence of a rubber whereby a high gloss, high impact vinyl aromatic polymer is obtained.
For many applications of vinyl aromatic polymers, it is highly desirable to have a high surface gloss on the finished product. In many instances, the conventional vinyl aromatic hydrocarbon homopolymers and high impact vinyl aromatic polymers cannot provide the desired gloss. When such occurs, it becomes necessary to use some other type of polymer such as ABS or SAN in place of the much less expensive general purpose and high impact polymeric vinyl aromatics. Therefore, it is desirable to have means for obtaining high gloss in the more usual and less expensive grades of vinyl aromatic polymers. For this reason, there is a continuing search for ways to improve the gloss in the general purpose and high impact vinyl aromatic polymers, without consequent loss of other desirable characteristics of processing properties.
In the polymerization of vinyl aromatic hydrocarbons such as styrene in the presence of a rubber to produce high impact polymers, it has been a practice to employ a chain transfer agent to control the molecular weight of the resulting polymer. Among the chain transfer agents employed are certain mercaptans such as tertiary dodecyl mercaptan and the like. The chain transfer agent customarily is added to the rubber-vinyl aromatic hydrocarbon solution at or prior to the beginning of polymerization. However, the prior art techniques of incorporating these chain transfer agents have resulted in an increasing of the rubber particle size which, consequently, yield a polymerized product exhibiting inferior gloss.
The prior art has recognized certain advantages to incremental addition of the chain transfer agent during the polymerization process. This technique provides addition of less than half of the total amount in a first increment followed by addition of the remainder at some further stage of polymerization in one or more further steps. These prior art techniques have typically been predicted upon the percent of conversion as indicative of the proper time for addition of the second increment with little regard for other properties of the reaction mass. While such techniques have been effective in improving melt flow properties, impact strength as well as other processing characteristics have been diminished, if not completely forfeited. Yet other prior art processes make similar incremental additions with no provisions for the absolute time of addition, the time varying depending upon the polymerization process involved. Exemplary of the latter is U.S. Pat. No. 3,428,712.
It is an object of present invention to provide a new and improved process for the preparation of high impact vinyl aromatic polymers whereby polymers of higher gloss are obtained.
Another object of the present invention is to provide a new and improved high gloss, high impact vinyl aromatic polymer.
An additional object of the present invention is to provide a method for imparting high gloss characteristics to high impact vinyl aromatic polymers.
A specific object of the present invention is to provide a new and novel process for preparing a high gloss, high impact polystyrene.
An additional specific object of the present invention is to provide a new high gloss, high impact polystyrene.
It is yet another object of the present invention to provide a method for the preparation of high impact vinyl aromatic polymers of improved gloss without the need to sacrifice melt flow or other processing properties.
Additional objects will become apparent from the following description of the invention herein disclosed.